tty: serial: imx.c: Reset UART before activating interrupts

If the UART has been in use before this driver was loaded, IRQs might be
active and get fired as soon as we set the handler, which will crash
in the spin_lock_irqsave(&sport->port.lock, flags) because port.lock is
not initialized until the port is added at the end of probe.

Signed-off-by: David Jander <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/imx.c

···
 /* half the RX buffer size */
 #define CTSTL 16
 
+static inline void imx_reset(struct imx_port *sport)
+{
+	int i = 100;
+	unsigned long temp;
+
+	temp = readl(sport->port.membase + UCR2);
+	temp &= ~UCR2_SRST;
+	writel(temp, sport->port.membase + UCR2);
+
+	while (!(readl(sport->port.membase + UCR2) & UCR2_SRST) && (--i > 0))
+		udelay(1);
+}
+
 static int imx_startup(struct uart_port *port)
 {
 	struct imx_port *sport = (struct imx_port *)port;
-	int retval, i;
+	int retval;
 	unsigned long flags, temp;
 
 	retval = clk_prepare_enable(sport->clk_per);
···
 
 	spin_lock_irqsave(&sport->port.lock, flags);
 	/* Reset fifo's and state machines */
-	i = 100;
-
-	temp = readl(sport->port.membase + UCR2);
-	temp &= ~UCR2_SRST;
-	writel(temp, sport->port.membase + UCR2);
-
-	while (!(readl(sport->port.membase + UCR2) & UCR2_SRST) && (--i > 0))
-		udelay(1);
+	imx_reset(sport);
 
 	/*
 	 * Finally, clear and enable interrupts
···
 	writel_relaxed(reg, sport->port.membase + UCR1);
 
 	clk_disable_unprepare(sport->clk_ipg);
+
+	/*
+	 * Perform a complete reset of the UART device. Needed if we don't
+	 * come straight out of reset.
+	 */
+	writel(0, sport->port.membase + UCR2);
+	writel(0, sport->port.membase + UCR1);
+	imx_reset(sport);
 
 	/*
 	 * Allocate the IRQ(s) i.MX1 has three interrupts whereas later